T2 contrast is one of the most commonly used tools for non-invasive diagnosis and prognosis of pathologies. Although T2 assessment is usually done in a visually qualitative manner, its quantitative characterization holds valuable information for numerous applications. These applications include the detection of biochemical and biophysical changes in hip and knee cartilage, diagnosis of prostate and liver cancer, assessment of diseased and post-transplant myocardial edema, the investigation of muscle physiology, for example, as well as many other applications.
Problems exist with the current methods of quantifying T2 relaxation times. Genuine quantification of T2 remains highly challenging in clinical practice due to long scan times associated with full single-echo spin-echo (“SE”) acquisitions, which can be on the order of dozens of minutes.
Quantification of true underlying T2 relaxation times is rendered difficult for fast multi spin-echo sequences (“MSE”) due to an inherent bias of the calculated T2 values resulting from contamination of a train of echoes by stimulated and indirect echoes, as shown in FIG. 1a. The difficulty is exacerbated because a train of spin-echoes, sampled at intervals of Δt, will not obey a theoretical exponential decay as shown in Equation 1:Signal(t=n·Δt)=Signal(0)×e−(n·Δt)/T2n=0,1,2 . . . ,N  (Eq. 1)Instead, the train will be distorted by the accumulated effect of recurring echoes that originate from earlier parts of the echo train.
Further complications ensue because most fast quantification methods are additionally sensitive to main (“B0”) and transmit (“B1”) field inhomogeneities, non-rectangular slice profiles, and diffusion weighting. Several approaches have recently been proposed for overcoming such artifacts using either analytical or numerical stepwise tracing of all coherence pathways arising in a multi-echo sequence. Some of these methods appear to show promising preliminary results. However, these approaches suffer from at least one of the following limiting aspects: they entail high numerical complexity, do not allow straightforward deduction of a T2 value from an experimentally measured train of echoes, fail to account for T1 or T2 relaxation during the radio-frequency (“RF”) pulse application, and generally do not account for all relevant experimental factors.
A need exists for improved technology, including technology that may address the above described disadvantages.